Polyurethanes have superior properties such as mechanical properties, abrasion resistance, elasticity recovery properties, oil resistance, flexibility and the like, and can be easily melt-molded. For this reason, polyurethanes have been widely used as alternative materials of conventional synthetic rubber or plastics.
However, polyurethanes exhibit strong stickiness. For this reason, for example, in the case of manufacturing a molded body by means of injection molding, problems easily occur such as poor release from a mold, poor outer appearance of a molded body caused by flow spots of a resin in a mold such as occurrences of air bubbles or flow patterns, conglutination among the obtained molded bodies, and the like. In addition, in the case of manufacturing a film or sheet by means of extrusion molding or the like, it is difficult to roll up the film or sheet itself, and for this reason, a mold release agent or an release coated paper (mold release sheet) must be used together therewith. If the film or sheet is rolled up itself without using a mold release agent or an release coated paper, it becomes difficult to roll out the rolled film or sheet. In addition, polyurethanes exhibit poor hot-water resistance or poor weather resistance.
For this reason, although polyurethanes have the aforementioned superior properties, the usage range thereof is restricted under present circumstances.
Silicones exhibit good mold release properties, have increased thermal resistance, cold resistance and weather resistance, exhibit superior water repellency and electrical insulation properties, and express stable physical properties even at widely ranging temperatures. In view of this, silicones have been used in various fields by utilizing the aforementioned properties.
However, silicones have disadvantages such as poor mechanical properties, or poor abrasion resistance, and the usage range thereof is restricted under present circumstances.
Recently, in order to compensate the disadvantages of both polyurethanes and silicones, composite molded bodies in which polyurethanes and silicones are compounded have been developed. The composite molded bodies are applied to, for example, key sheet for use in push-button switches of mobile phones, personal electronics, automobile parts, communication devices, and the like.
However, molded bodies or layers obtained from polyurethanes exhibit insufficient surface activities. For this reason, in the case of laminating silicones, the surface of the molded bodies or layers must be preliminarily subjected to a surface-activation treatment. As the aforementioned surface-activation treatment, a primer treatment, a corona discharge treatment, a plasma treatment, an ozone treatment, a flame treatment or the like is known. However, there is a problem in that a reduction of productivity or reduction of work efficiency may be caused by any of the means described above.
In order to solve the aforementioned problems, a process for integral-molding thermoplastic resins and silicone resins by means of an injection molding machine is proposed (Patent Document 1). In addition, a coating agent of a polyurethane in which adhesion to a silicone rubber is improved is proposed (Patent Documents 2 to 4).
However, in the case of using a polyurethane as the thermoplastic resin in the process described in Patent Document 1 and in the coating agents described in Patent Documents 2 to 4, adhesion between polyurethanes and silicones is insufficient, and for this reason, a composite molded body which combine both superior properties of polyurethanes and silicones can not be obtained.